This invention relates to an optical assembly for use in a barcode reader and, in particular, to an optical assembly that is capable of maximizing the light produced by a plurality of light emitting diodes to provide a high intensity image of a barcode target at the image recording surface of a solid state imager.
Although the advantages associated with light emitting diodes (LEDs) when used in barcode scanning equipment are well known, the level of the intensity produced by this type of lamp is relatively low when compared to other light sources such as halogen lamps or arc lamps. In an effort to improve the effectiveness of light emitting diodes in this application, it is sometimes customary to employ a relatively large number of lamps aligned in one or more rows above or below the imaging lens. As a result, the target region, as well as the periphery of the target region, are flooded with an excessive amount of light. This approach, however, is space consuming and poses certain assembly and alignment problems.
Optical units have also been devised for providing coplanar illumination wherein the light emitting diodes are mounted in the same plane as the imaging onto both sides of the imaging lens. The light from the light emitting diodes is further passed through magnifying lens to project the light onto the target region. Additionally, diffusers are used in association with the LEDs to more uniformly distribute the light within the target area. Here again, these optical units overcome many of the problems associated with LED illumination systems. They nevertheless pose certain other problems relating to bringing the components together in assembly to provide a compact, easy to install and adjust unit suitable for use in a hand-held long range scanner as opposed to a scanner that reads barcodes in contact.